On the occasion of the celebration of Jim Cronin’s life on September 30, 2016 came up the idea to gather individual recollections and stories [http://astro.uchicago.edu/Cronin/memories.php] about Jim and the Auger Observatory over the years.

Below are some recollections from Paul Mantsch (Scientist Emeritus at Fermilab), former spokesperon of the US Auger Collaboration and close friend to Jim.

Jim Cronin and the Pierre Auger Observatory

Paul Mantsch – 30 August 2016

It was a great privilege and honor to work with Jim Cronin on the Pierre Auger Observatory. What follows are some of my recollections of the events that, under Jim’s inspired leadership, led to the construction and operation the world’s largest cosmic ray observatory.

It was late fall of 1993, a few weeks after the US congress had terminated the Supercollider. Having invested eleven of my most productive years on the SSC beginning with its conception in June of 1982, I was still recovering. However, what came next was exciting and in the end much more rewarding, the defining challenge of my scientific life. I remember the day clearly, as it set my course for the next twenty-two years. I heard that Jim Cronin had just visited Fermilab’s director, John Peoples and discussed the possibility of Fermilab hosting a workshop to design a huge cosmic ray air shower detector, ten times bigger than anything built up to that time. The new cosmic ray detector would record particles hitting the earth from space with energies 10 million times more energetic than even the Supercollider would have produced. Now this news instantly struck a responsive chord as I had a latent interest in cosmic ray physics since my undergraduate experience working part time in the Cosmic Ray Laboratory at Case. On hearing of Jim’s idea, I knew instantly that I had to be part of this new, exciting project. I knew Jim slightly and wasted no time finding a phone, calling him and offering help. Jim was obviously pleased and a few days later came to Fermilab to discuss his ideas with small group of like-minded colleagues I had rounded up. I remember our asking lots of questions about how one would possibly measure the properties of cosmic rays by detecting a few particles that reached the ground. Jim explained all of this with great enthusiasm and later sent us a stack of papers, including those from a recent cosmic ray conference in Paris. We were hooked. Poring over the papers, we were soon excitedly imagining designs for cosmic ray particle detectors that could be spread over thousands of square kilometers to capture these strange messengers from the cosmos. The idea of a very large cosmic ray detector had been germinating for several years. In 1991 Jim Cronin, who had developed an interest in cosmic ray physics and Alan Watson, a long time cosmic ray physicist from the University of Leeds got together at in international cosmic ray conference in Dublin. They concluded that the only way to address the cosmic ray questions head on was to build a huge array of detectors, perhaps 5000 square kilometers in area, which would have a chance of gathering enough cosmic ray events above 1019 electron volts to provide some answers. The Giant Array Project was born.The project gathered headway over the next few years as Cronin and Watson described their vision in talks at meetings all over the world where cosmic ray physics was on the agenda, including cosmic ray conferences in Adelaide in 1990 and then in Paris in 1993. By the time Cronin visited Fermilab in late 1993 the idea was beginning to take on a serious form. Cronin’s idea for a six-month Giant Array Project design workshop at Fermilab was inspired. The workshop would be open to researchers in the cosmic ray physics community and related fields, some to share their insights and experience and others who might want to be part of the project. All could participate in the planning the Observatory from the beginning, equal partners in developing the design. We began planning the Giant Array Project workshop during 1994 with the approval and encouragement of the Fermilab director and the help of the Fermilab staff. I organized the details of the workshop while Cronin started inviting researchers from around the world to participate, noted experts in astrophysics and cosmology both theorists and experimentalists who would bring their knowledge to help shape the design. Visitors would come a few days or a few months to exchange ideas and refine the design. With his reputation (and charm) Jim was able to attract researchers from 40 universities and laboratories from Argentina, Armenia, Australia, Bolivia, Brazil, Czech Republic, China, Greece, Italy, Mexico, Poland, Romania, Slovenia, the UK and, of course, the US. It was an eclectic group of high-energy physicists, nuclear physicists, cosmic ray physicists, and astronomers. Many of these countries had a tradition of cosmic ray physics but often did not have the means to participate in the costly world of high-energy physics accelerators. The excitement associated with the power of the unique international collaboration that was forming began to sink in when toward the end of the workshop when Jim and I discussed possible involvement of groups from many countries from around the world, talking individually to research groups from each of the countries that attended. As more detailed objectives and requirements of the project began to take shape, competing design approaches evolved. Our approach to the design was to allow a “thousand flowers bloom” then choose the best design ideas among them. Indeed, there were many ideas. With the help of some Fermilab colleagues, I had built two 32 square foot prototype detectors using large of sheets of scrounged scintillation plastic. My Fermilab colleague, Peter Mazur, designed detectors using a technique involving resistive plate chambers. Another group in France was working on scintillator/lead/scintillator sandwich, which become known as the leadburger. Alan Watson argued for a water Cerenkov detector similar to the one he had used at his Havarah Park array in the 1970s and 1980s. After a close look at the costs and the likely performance of the different candidate detectors, we decided on simple, proven, water Cerenkov detectors, which were also quite benign to the environment. After more discussion, we decided to augment the water detectors with air fluorescence detectors, a technique that had been pioneered by the University of Utah for their Fly’s Eye detector. There would be two sites, one in the northern hemisphere and one in the southern hemisphere so that, as the earth turned the Observatory would gather cosmic ray events from the whole sky. During the workshop, someone suggested that the name Giant Array Project lacked style and that it would be better to name the Observatory after Pierre Auger in recognition of his beautiful, pioneering cosmic ray experiments. The collaboration quickly adopted the name and we launched the Pierre Auger Project to build the Pierre Auger Observatory. The ideas developed in the workshop were summarized in the Pierre Auger Observatory Design Report. The design report included a complete design and a detailed cost estimate for both the construction and operation of the Observatory. The Observatory in Argentina was built almost exactly as described in the design report and, in retrospect, it was so successful were we to start again, we would change little. A possible improvement would have been to make it even bigger. The collaboration that emerged during and after the design workshop now consisted of about 69 institutions in 17 countries spread over Europe, North and South America and Australia. No country dominated with the maximum contribution of any one country to construction being less than 25%. Another feature, and a concern of some, was that the project was not anchored to some strong institution that could provide financial stability as that enjoyed by the big collider detectors at established national high-energy physics laboratories. Indeed a suitable model for such an international partnership did not exist. The collaboration we were organizing for the Auger Project was unique. Most of the collaborators were not used to the discipline required for a project of this scale and many, if not most, were deeply suspicious of what they perceived as mostly unnecessary, indeed counter-productive, bureaucracy. One of those was Jim Cronin. Like Jim, most collaborators were used to working with small groups of five to ten researchers with no real organization so that the research team could communicate daily and make decisions easily.I drew up the organization chart based on what I had learned about managing projects over the years at Fermilab and in the SSC work. I gave it to Jim who reluctantly showed it to the developing collaboration at the workshop, beginning his talk with: “I am really embarrassed to show this.” In time, Jim would come to appreciate the basic need for the organization, particularly as building the Observatory evolved. Jim was the obvious choice for spokesperson. I was hoping that he would ask me to be co-spokesperson. However, having accepted my arguments for the need for a workable project management, Jim was certain that I should be project manager. I later regretted the designation project manager as reporters assumed that I was someone with a shovel and yellow hardhat. Mostly as the result of Dilbert cartoons, the term manager and management have assumed distinctly negative connotations. Nevertheless, I bore this title for the next 20 years.The search for a suitable site got underway almost immediately after the Fermilab workshop using funds from a grant that Jim Cronin was able to obtain from William Grainger, a Chicago industrialist and from UNESCO. With the physical site requirements developed during the workshop in hand, a team of collaborators evaluated prospective northern hemisphere sites in Argentina, Australia and South Africa. Northern hemisphere site possibilities included Mexico, Spain and Utah and Colorado in the US. The site selection was based primarily on these requirements and on the scientific support from the host country. The evaluation team used a set of instruments to evaluate the clarity of the sky, an essential consideration for the fluorescence detectors, by measuring the atmospheric attenuation of star light. An important, but secondary, consideration was the value of incentives that a potential host might offer. Having a design in hand and with some suitable sites identified, the next task was to decide on the final sites, form a collaboration and then persuade the funding agencies in the collaborating countries that they should approve and share in the $100 million cost. The process turned out to be both lengthy and painful. In November of 1995, UNESCO also hosted the first Auger collaboration meeting at its headquarters in Paris where the collaboration was formed and the site was selected for the observatory in the southern hemisphere. An Auger Collaboration Board was formed that included representatives of the institutions of those countries that attended the meeting.The site was selected by an election, with each country in the new collaboration having one vote. After an extensive discussion Argentina was selected, both because of the enthusiastic support of scientists there, led by Alberto Etchegoyen, the generous offer of funds and a suitable site to be offered by the president of Argentina, President Carlos Menem who had succumbed to Jim Cronin’s persuasion (and charm) in an earlier visit to Buenos Aires.We finally had a good look at the site in Argentina during a visit in September 1996 at a collaboration meeting set at a small resort near the city of San Rafael. The meeting was not far from vast open plain called the Pampa Amarilla (yellow pampa) where we soon would deploy our detectors over an expanse of 1000 square miles of flat dry land. After a tense period of finding the necessary funds involving sometimes painful reviews, we prevailed for the Argentina site, due in large measure to Jim Cronin’s boundless energy and enthusiasm. Prototype detectors began to appear that the site in 2000 with serious construction beginning in 2002. The first data taking began in 2004 even before the Observatory was completed in 2008. More than 64 journal papers have been published based on Auger data that is shaping the future of astroparticle physics. At least as important is the training of young physicists for the future. From among the Auger collaborators, 267 PhDs have been awarded with more than 100 more in the pipeline.

While Jim Cronin has a large and stellar scientific legacy, the Pierre Auger Observatory will be one of the brightest stars.